1. Field of the Invention
The present invention relates to an antenna. More particularly, the present invention relates to a leaky-wave antenna capable of multi-plane scanning.
2. Description of Related Art
With booming development of wireless communication technology and liberalization of telecommunication, various communication protocol specifications and techniques are provided for achieving a better communication quality in an effective bandwidth. Moreover, since an antenna is one of indispensable elements in a wireless communication system, to design an antenna capable of improving a system performance is an important issue.
In a current communication system, the antenna generally has a characteristic of a wide beam pattern, for example, an omni directional and single beam. Generally, signals transmitted by an omni directional antenna and a directional antenna are liable to be influenced by multi-path fading and similar signals, so that a communication quality is influenced. To resolve the above problem, development of a smart antenna is one of the most promising technologies. Generally, the smart antennas can be group into switched beam antennas and scanning beam antennas. The switched beam antenna can change a beam shape and a beam direction of the antenna to increase an antenna gain and reduce the noise interference. The scanning beam antenna is implemented with assistant of active components or implemented by a leaky-wave antenna.
Presently, it is known that designs of the switched-beam antenna or the scanning beam antenna are approximately categorized into following types. The first type is to use a 90-degree coupler to feed into an antenna array, and different ports of the coupler are changed to serve as an input port, so as to achieve a beam switching effect. The second type is to design a Yagi antenna, and a PIN diode is added into a parasitic device, so that a length of the parasitic device is changed according to whether the PIN diode is conducted for serving as a reflection device or a guided-wave device, so as to achieve an effect of switching the beam direction. The third type is to use a Butler matrix to match an antenna array, and use a beam-forming technique for implementation.
Although the current techniques can achieve the beam switching effect, there is a plurality of shortages. For example, regarding the technique of changing different ports of the coupler to serve as the input port, the unused ports have to be connected with matched impedances for normal operation, which may lead to an operation inconvenience. Regarding the Yagi antenna designed according to a monopole antenna technique, etc., the antenna does not have a low profile characteristic, and slimness of the antenna cannot be implemented. Moreover, regarding the beam-forming technique, a complicated and large-area feed-in network and an antenna array have to be used to implement switching of the multiple beam directions, so that miniaturization thereof is hard to be achieved. Moreover, none of the above methods can achieve a beam scanning function.